1. Field of the Invention
This invention relates to a process for the production of bulky alkyldiarylphosphines and unsymmetrical dialkylarylphosphines. More particularly, this invention relates to the use of Grignard reagents to produce these compounds from aryldichlorophosphines.
2. Description of the Prior Art
Aryldialkylphosphines and alkyldiarylphosphines are known to be useful as promoters of rhodium-based catalysts for the hydroformylation of olefins to aldehydes. For example, U.S. Pat. No. 4,283,562 discloses a rhodium-catalyzed hydroformylation process wherein improved catalyst stability is achieved by using as the phosphine ligand a branched-chain alkyldiphenylphosphine, a branched-chain dialkylphenylphosphine, a cycloalkyldiphenylphosphine or a dicycloalkylphenylphosphine.
Alkyldiarylphosphines (RPAr.sub.2) and aryldialkylphosphines (R.sub.2 PAr) may be produced by reacting chlorophosphine precursors, such as chlorodiarylphosphines (ClPAr.sub.2) and aryldichlorophosphines (Cl.sub.2 PAr), with alkylorganometallic compounds (RM), such as a Grignard reagent, as shown in equations (1) and (2): EQU RM+ClPAr.sub.2 .fwdarw.RPAr.sub.2 +MCl (1) EQU 2RM+Cl.sub.2 PAr.fwdarw.R.sub.2 PAr+2MCl (2)
wherein
M=Mg halide, for example PA1 R=alkyl PA1 Ar=Aryl
Unfortunately, since even simple chlorodiarylphosphines are quite expensive, it is difficult to economically produce commercial quantities of the alkyldiarylphosphines from such chlorodiarylphosphines. However, aryldichlorophosphines, such as phenyldichlorophosphine, are available commercially at lower cost than chlorodiarylphosphines. Moreover, aryldichlorophosphines may be manufactured by the Michaelis modification of the Friedel-Crafts reaction as described in Journal of the American Chemical Society 73, pp. 755-56 (1951) and as represented by the following equations (3) and (4): EQU ArH+PCl.sub.3 +AlCl.sub.3 .fwdarw.ArPCl.sub.2.AlCl.sub.3 +HCl (3) EQU ArPCl.sub.2.AlCl.sub.3 +OPCl.sub.3 .fwdarw.ArPCl.sub.2 +Cl.sub.3 AlOPCl.sub.3 ( 4)
wherein Ar=aryl
Scherer and Gick report (Chem. Ber. 103, 71-75, 1970) that neither t-butylmagnesium chloride (t-BuMgCl), nor methylmagnesium iodide, when reacted with methyldichlorophosphine (MePCl.sub.2) produce pure methyl-t-butylchlorophosphine. However, the same authors subsequently reported a 45% yield of product from the MePCl.sub.2 /t-BuMgCl route at -20.degree. C. (Z. Naturforsch. B 25(8), 891-92, 1970). Similar compounds, ethyl-t-butylchlorophosphine, ethylisopropylchlorophosphine, and isopropyl-t-butylchlorophosphine, have been synthesized from ethyldichlorophosphine, t-butyldichlorophosphine, isopropylmagnesium dichloride and t-butylmagnesium chloride (J.C.S. Dalton 638-644, 1980).
It is known that the reaction of one equivalent of phenyl-Grignard reagent, PhMgX, with phenyldichlorophosphine, PhPCl.sub.2, does not selectively form chlorodiphenylphosphine, Ph.sub.2 PCl. In fact, reports on the synthesis of chlorodiarylphosphines from aryldichlorophosphines usually employ organometallic compounds far less reactive than Grignard reagents such as organomercury, organocadmium or organozinc reagents to induce selectivity to chlorodiphenylphosphine formation. (k. Sasse, in E. Muller, "Methoden der Organischen Chemie (Houben-Weyl)" 4th ed., Vol. 12, Part I, Georg Thieme Verlag, Stuttgart, 1963, pp. 203-205). In another reference (J.C.S. C 1930-33, 1971), it is reported that t-butyldiphenylphosphine, t-BuPh.sub.2 P, may be prepared by first producing and isolating chlorophenyl-t-butylphosphine, t-BuPhPCl (by reacting phenyldichlorophosphine, PhPCl.sub.2, and t-BuMgCl), and then reacting the t-BuPhPCl with an aryllithium (specifically, phenyllithium, PhLi). These reactions may be represented by the following equations (5) and (6): EQU PhPCl.sub.2 +t-BuMgCl.fwdarw.t-BuPhPCl+MgCl.sub.2 ( 5) EQU t-BuPhPCl+PhLi.fwdarw.t-BuPh.sub.2 P+LiCl (6)
This technique suffers from the disadvantage caused by the additional intermediate isolation step.
D. Jore et al., in J. Organometal. Chem. 149, C7-C9 (1978), report that unsymmetrical dialkylphenylphosphines, PhPRR', can be produced from phenyldichlorophosphine, PhPCl.sub.2, by first adding an organometallic compound less reactive than Grignard reagents, such as an organocadmium reagent R.sub.2 Cd (R=Me or PhCH.sub.2), to the PhPCl.sub.2 and then adding an organometallic reagent R'M (R'=PhCH.sub.2, CH.sub.3 or o-CH.sub.3 C.sub.6 H.sub.4 ; M not being specified), according to the following equations (7) and (8): EQU PhPCl.sub.2 +1/2R.sub.2 Cd.fwdarw.PhP(Cl)R (7) EQU PhP(Cl)R+R'M.fwdarw.PhPRR' (8)
The disadvantage of this method is that the organocadmium reagent is fairly exotic and is expensive to prepare. For example, it is commonly prepared from a methyllithium reagent, MeLi, according to equation (9): EQU 2MeLi+CdCl.sub.2 .fwdarw.Me.sub.2 Cd+2LiCl (9)
The use of CdCl.sub.2 and methyllithium (or other organometallic or Grignard reagents) to obtain the organocadmium is economically unattractive for commercial production of phosphines.
A similar approach to triarylphosphines by the sequential additions of two different arylorganometallics to phenyldichlorophosphine was reported by G. Wittig et al. in Liebig's Ann. Chem. 851 17-26 (1971). The disclosed process can be described by the following equation (10): ##STR1## This method is also not economically attractive for the same reasons.
Another known process to prepare alkylarylchlorophosphines comprises reacting Grignards and phenyldichlorophosphine, purifying the reaction product by distillation, and then adding a second Grignard reagent to prepare tertiary phosphines. A process of this type is disclosed in U.S. Pat. Nos. 3,804,950 and 3,755,459. J. R. Corfield, et al. (J. Chem. Soc. C 1930-1933, 1971) have synthesized and isolated t-butylphenylchlorophosphine. The isolated t-butylchlorophenylphosphine is reacted with aryllithium reagents, either phenyllithium or alpha-naphthyllithium to produce t-butyldiphenylphosphine or t-butyl-alpha-naphthylphenyl-phosphine, respectively. The disadvantage of these two methods is the isolation of the alkylarylchlorophosphine intermediates. This approach also makes such methods much less commercially inviting, especially since the alkylarylchlorophosphines are difficult to manipulate due to their extreme air and hydrolytic sensitivities.
Another route to phosphines employs a dialkylamino substituent, R.sub.2 N, on phosphorus as a blocking group. For example, R.sub.2 NPCl.sub.2 can be prepared from the reaction of two moles of R.sub.2 NH with one mole of PCl.sub.3. The P--Cl bonds in R.sub.2 NPCl.sub.2 are reactive towards Grignards, the N--P bond is not. However, upon treatment with anhydrous hydrogen halides the N--P bond is replaced with a P-halogen bond, which is suitable for Grignard substitution.
U.S. Pat. No. 2,934,564 relates to compounds of the general formula R.sub.2 PX wherein R represents an alkyl or aryl group and X represents chlorine, bromine or iodine. For example, the reaction of Me.sub.2 NPCl.sub.2 (0.42 mole) with p-tolylmagnesium bromide (0.84 mole) produces dimethylamino-di-p-tolylphosphine. The isolated dimethylamino-di-p-tolylphosphine (31.88 mmoles) was treated with 1428 cc (63.75 mmoles) of anhydrous HCl yielding di-p-tolylchlorophosphine, which was purified by distillation. Similarly, Burg, et al. (J.A.C.S. 80, 1107-09, 1958) disclose the preparation of chlorodimethylphosphine from Me.sub.2 NPCl.sub.2 and suggest the viability of a Grignard route to R.sub.2 PR'-type phosphines. K. Issleib, et al. (Chem. Berichte 29, 2682-3008, 1959) have shown that Et.sub.2 NPCl.sub.2 (Et=ethyl) and cyclohexylmagnesium chloride react in a 1:1.25 molar ratio to form diethylaminocyclohexylchlorophosphine in 57.5% yield. The authors suggest this reaction can be exploited to prepare unsymmetrical chlorophosphines of the type RR'PCl, but no mention is made of the possibility of further reaction to unsymmetrical tertiary phosphines of the type RR'R"P.
All routes using dialkylaminochlorophosphines, R.sub.2 NPCl.sub.2, are tedious and not commercially attractive since (1) R.sub.2 NPCl.sub.2 must be generated from PCl.sub.3 and R.sub.2 NH and subsequently purified, (2) the Grignard is reacted with R.sub.2 NPCl.sub.2 and the intermediate R.sub.2 NPRCl or R.sub.2 NPR.sub.2 is isolated, (3) R.sub.2 NPRCl or R.sub.2 NPR.sub.2 is converted with HCl to RPCl.sub.2 or R.sub.2 PCl and then isolated, and (4) RPCl.sub.2 or R.sub.2 PCl is finally reacted with another Grignard to afford the tertiary phosphines.
Another route to unsymmetrical phosphines R.sub.2 PR' through the reaction of PCl.sub.3 with mixtures of RMgBr and R'MgBr in stoichiometric proportions of reactants (1:2:1) produces a mixture of tertiary phosphines which cannot be separated into its components either by crystallization or by chromatography (N. A. Rozanel 'Skaya, et al., Journal of General Chemistry of the USSR-English Translation 48 (8) 1732-1733, 1978).
The prior art also discloses methods for selectively preparing dichloroalkylphosphines and chlorodialkylphosphines from alkylmagnesium chlorides and phosphorus trichloride. For example, W. Voskuil, et al. [Rec. Trav. Chim. 82, 302-304 (1963) and "Organic Syntheses" Vol. 5, pp. 211-214 (1973)] have reported procedures for preparing these compounds. In addition, they list the necessary conditions for obtaining pure chlorophosphines. Subsequently, chlorodineopentylphosphine and dichloroneopentylphosphine have been similarly prepared (R. B. King, et al., J. Org. Chem. 41 (6) 972-977, 1976).